Abstract 3837: Defining the mechanism of semaphorin4D tumorigenesis in prostate cancer models

Background: Advanced and recurrent prostate cancer exhibits a “cold” immune phenotype characterized by an influx of immunosuppressive cells and fewer tumor-infiltrating lymphocytes (TILs), limiting the efficacy of checkpoint inhibitors. Semaphorin4D (SEMA4D/CD100), via the PlexinB receptors, regulates cell-cell interactions and migration in the nervous system, also responsible for cancer metastasis. Further, SEMA4D affects angiogenesis and immune regulation in other cancers. We hypothesize that SEMA4D promotes the recruitment of immunosuppressive cells via tumor blood vessels, further impairing TIL activity and anti-tumor immunity. Loss of SEMA4D function could disrupt vascularization, creating hypoxia that induces tumor cell apoptosis. Methods: Two mouse models—subcutaneous Myc-CaP allografts in immunocompetent mice and Hi-Myc prostate cancer GEMM were treated with a SEMA4D blocking mAb (pepinemab) to inhibit SEMA4D signaling. Tumor volume changes, vascularity, and oxygen saturation were assessed during treatment using high-frequency ultrasound, Power doppler, and photoacoustic imaging followed by FACS and IHC analyses on tumor tissues to evaluate immune cell phenotypes, hypoxia, apoptosis, and microvascular damage. To further elucidate genotypic changes in the tumor immune microenvironment, RNA sequencing gene expression changes associated with SEMA4D inhibition, including signaling pathways and Immune cell constituents. Results: Blocking SEMA4D significantly arrested tumor growth and reduced vasculature in Hi-Myc mice, with no prominent changes in immune phenotype by FACS after 4 weeks pepinemab treatment. IHC will test for changes in hypoxia, apoptosis, and microvascular damage. Allografts of prostate tumor cells similarly demonstrated tumor growth arrest. Effects on vasculature and microvascular integrity, leading to hypoxia and apoptosis, in this more tractable imaging environment, are anticipated. Transcriptomically, gene ontology and enrichment analyses may reveal pathways related to vessel formation, immune regulation, and metastasis. Conclusion: Our findings suggest that SEMA4D inhibition effectively arrests tumor growth by disrupting angiogenesis and potentially regulating immune activity, alongside inducing hypoxia and apoptosis. Ongoing transcriptomic analyses will further explore molecular mechanisms, including pathways involved in angiogenesis and immune regulation. Citation Format: Kavin Velur Ganesan, Maolake Aerken, Renyuan Zhang, Kent L. Nastiuk. Defining the mechanism of semaphorin4D tumorigenesis in prostate cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3837.